This invention generally relates to apparatuses for applying a coating material to at least one continuous zone of a substrate, for example, to both sides of a long strip of material. More specifically, the present invention is directed to a coating apparatus having a plurality of metering devices for controlling the amount of coating material being supplied to at least one liquid-wicking solid body, for example, a pair of strips, from which the coating material is transferred, optionally indirectly, to the substrate zone to be coated. The invention will be further described below primarily in connection with use on a long continuous web of substrate material, but it should be understood that it is, mutatis mutandis, more widely applicable to other substrates.
Currently, numerous methods exist for applying a coating or thin film of material to a sheet or strip of material. One conventional method of coating a continuous strip of sheet material is to submerse the sheet material in a bath of the coating material. This can be accomplished by pulling the sheet material through the bath of coating material, and then wiping off any excess coating material. This method has many drawbacks. One drawback to this method is the difficulty to control the amount of coating material applied to each side of the sheet material. Another drawback is the inability to apply different coating materials to each side of the sheet material. Also, this method often wastes a certain amount of the coating material during the wiping step.
Another method of applying a coating or thin film of material to a sheet or strip of material is to employ a spray coater or atomizer. In such a method, the coating material is electrostatically disposed on the sheet material. A spray coater in accordance with this method is disclosed in U.S. Pat. No. 4,839,202.
Still other types of coating methods include passing the sheet material through various applicators which deposit a thin film onto the sheet material with or without electrostatic assistance. The applicators can be either stationary members or rotatable members. One example of such a coating apparatus, which uses a pair of oppositely disposed applicators, is disclosed in U.S. Pat. No. 5,549,752 to Hahn et al. The Hahn patent discloses passing a continuous strip of material between a pair of oppositely disposed applicators for applying a thin film thereto. In one embodiment, two stationary wicks directly contact the sides of the continuous strip of material to apply a coating to both sides of the sheet material. In another embodiment, the wicks apply the coating material to two feed rolls which contact the sides of the sheet material to apply a thin film of coating material thereto. One drawback to this type of coating apparatus is that it lacks the ability to adjust the amount of coating material being supplied to various sections of the applicators.
Other examples of prior coating apparatuses are disclosed in U.S. Pat. Nos.: 4,601,918 to Zaman et al.; 4,604,300 to Keys et al.; 4,712,507 to Helling; and 4,995,934 to Janatka.
In view of the above, it will be apparent to those skilled in the art that there exists a need for an improved coating apparatus which utilizes a plurality of metering devices to control the flow of coating material to the applicators for obtaining the desired coating on a pair of opposed sides of a substrate or sheet material. This invention addresses this need in the art, along with other needs which will become apparent to those skilled in the art once given this disclosure.
One object of the present invention is to provide a coating apparatus which utilizes a plurality of metering devices to accurately control the amount of coating material being supplied to the applicators for controlling the amount of coating material being applied throughout the entire area of the zone of the substrate to be coated.
Another object of the present invention is to provide a coating apparatus that is relatively simple to manufacture, assemble and use.
Another object of the present invention is to provide a coating apparatus which can be employed in existing coating operations.
Still another object of the present invention is to provide a coating apparatus which is relatively inexpensive to manufacture.
The foregoing objects are basically attained by providing a coating apparatus for applying a coating material on at least one zone, and often at least two zones, of a substrate material, said apparatus comprising: at least one conveyor for a supply of coating material; at least one fluid-wicking solid body that is in fluid communication with any coating material present in at least said one conveyor therefor and also is in contact with the ambient atmosphere, unless some part of the zone of the substrate to be coated, or of a solid means for transferring coating material to some part of the zone of the substrate to be coated, is in contact with said fluid-wicking solid body; means for causing at least part of the zone of the substrate to be coated to come into contact for at least a part of the time during which the apparatus is used with at least one said fluid-wicking solid body; and a plurality of metering devices each of which Is in fluid communication with any supply of coating material that is present in at least one said conveyor therefor and at least a first group of said metering devices being in fluid communication with different portions of the same said fluid-wicking solid body.
Various objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.